Dietmar Geiger

University of Würzburg

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Rainer Hedrich

University of Würzburg

Tobias Maierhofer

University of Würzburg

Peter Ache

University of Würzburg

Khaled A. S. Al‐Rasheid

King Saud University

Dirk Becker

University of Würzburg

Irene Marten

University of Würzburg

Ingo Drèyer

University of Talca

M. Rob G. Roelfsema

University of Würzburg

Sönke Scherzer

University of Würzburg

Heike M. Müller

University of Würzburg

Cooperative Institutions

University of Würzburg

112

Leibniz Association

Max Planck Institute of Molecular Plant Physiology

Centre National de la Recherche Scientifique

Universitätsklinikum Würzburg

University of Freiburg

Max Planck Society

China Agricultural University

Consejo Superior de Investigaciones Científicas

University of Copenhagen

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A unified nomenclature of NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family members in plants

Trends in Plant Science (2013)

Sophie Léran Kranthi Varala Jean‐Christophe Boyer Maurizio Chiurazzi Nigel M. Crawford

Subfamily

Protein family

Homology

Solute carrier family

Phylogenetic nomenclature

10.1016/j.tplants.2013.08.008

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Citations (584)

Protein RS1 (RSC1A1) Downregulates the Exocytotic Pathway of Glucose Transporter SGLT1 at Low Intracellular Glucose via Inhibition of Ornithine Decarboxylase

Molecular Pharmacology (2016)

Chakravarthi Chintalapati Thorsten Keller Thomas D. Mueller Valentin Gorboulev Nadine Schäfer

Na+-d-glucose cotransporter 1 (SGLT1) is rate-limiting for glucose absorption in the small intestine. Shortly after intake of glucose-rich food, SGLT1 abundance in the luminal membrane of the small intestine is increased. This upregulation occurs via glucose-induced acceleration of the release of SGLT1-containing vesicles from the trans-Golgi network (TGN), which is regulated by a domain of protein RS1 (RSC1A1) named RS1-Reg. Dependent on phosphorylation, RS1-Reg blocks release of vesicles containing SGLT1 or concentrative nucleoside transporter 1. The hypothesis has been raised that RS1-Reg binds to different receptor proteins at the TGN, which trigger release of vesicles with different transporters. To identify the presumed receptor proteins, two-hybrid screening was performed. Interaction with ornithine decarboxylase 1 (ODC1), the rate-limiting enzyme of polyamine synthesis, was observed and verified by immunoprecipitation. Binding of RS1-Reg mutants to ODC1 was characterized using surface plasmon resonance. Inhibition of ODC1 activity by RS1-Reg mutants and the ODC1 inhibitor difluoromethylornithine (DFMO) was measured in the absence and presence of glucose. In addition, short-term effects of DFMO, RS1-Reg mutants, the ODC1 product putrescine, and/or glucose on SGLT1 expressed in oocytes of Xenopus laevis were investigated. High-affinity binding of RS1-Reg to ODC1 was demonstrated, and evidence for a glucose binding site in ODC1 was provided. Binding of RS1-Reg to ODC1 inhibits the enzymatic activity at low intracellular glucose, which is blunted at high intracellular glucose. The data suggest that generation of putrescine by ODC1 at the TGN stimulates release of SGLT1-containing vesicles. This indicates a biomedically important role of ODC1 in regulation of glucose homeostasis.

10.1124/mol.116.104521

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Citations (9)

Carbon assimilation and export in sugar beet leaves. [Beta vulgaris]

Plant Physiol., Suppl.; (United States) (1987)

Tucci Dietmar Geiger J. C. Servaites

Net carbon exchange rates (NCE), starch accumulation rates, gas exchange, and the maximum amount of carbon available for export were studied in Beta vulgaris L. following a 25% increase or a 25% decrease in ambient CO/sub 2/ (340 ..mu..l/L). Changing CO/sub 2/ by 25% above or below ambient had no effect on the ratio of internal CO/sub 2/ to ambient CO/sub 2/. Stomatal aperature adjusted in both cases to maintain the same relative stomatal limitation to NCE. Increasing CO/sub 2/ 25% increased NCE and water use efficiency, but slightly decreased stomatal conductance by 9% below leaves maintained at ambient. In contrast, a 25% reduction in CO/sub 2/ decreased NCE and water use efficiency. Decreasing CO/sub 2/ caused an increase in conductance also by 9%. Increasing CO/sub 2/ increased starch storage by 36%, but caused no change in the ratio of starch accumulation to NCE. A reduction in CO/sub 2/ caused a 60% decrease in the rate of starch storage and decreased the ratio of starch accumulation to NCE by one-half. The maximum amount of carbon available for export was increased 25% by increasing CO/sub 2/, but decreased by 5% following a reduction in CO2 level. These data are evidence thatmore » export rates are maintained at the expense of starch synthesis during periods of low NCE.« less

Stomatal Conductance

Carbon fibers

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Role of Ion Channels in Plants

Springer protocols handbooks/Springer protocols (2012)

Rainer Hedrich Dirk Becker Dietmar Geiger Irene Marten M. Rob G. Roelfsema

When the second patch-clamp book of Sakmann and Neher appeared in 1995 (Sakmann and Neher, Single-channel recording, 2nd edn. Plenum Press, New York, 1995), the molecular nature of plant ion channels was still in its infancy. Since 1995, various members of the Shaker-, Two-Pore-, and KCO-type potassium channels have been identified; and their cellular and subcellular localizations have been resolved. The function of major K+ channels has been characterized in its natural environment of plant cells and after heterologous expression. Just a few years ago, the first genes encoding plant plasma membrane anion channels were identified and shown to encode channels mediating Slow/SLAC-type and Rapid/QUAC-type currents. Distinct members of the potassium and anion channel families are involved in volume regulation, nutrient sensing, and uptake. Among them the K+ channel AKT1 and anion channel SLAC1 are addressed in a calcium-dependent manner. Thereby, protein kinase–channel interaction and transphosphorylation are the keys to channel opening. In contrast to animal cells, plant cells are equipped with a large central vacuole. This acidic internal organelle provides for dynamic storage of ions and nutrients. Using isolated vacuoles from the model plant Arabidopsis thaliana in combination with transient overexpression approaches, major and low abundant ion channels and transporters could be characterized. This chapter provides insights into the current state of the plant ion channel field and introduces new approaches with patch-clamping plant cells and vacuoles.

Heterologous expression

Plant cell

Shaker

10.1007/978-4-431-53993-3_19

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Citations (9)

Defensin-Like ZmES4 Mediates Pollen Tube Burst in Maize via Opening of the Potassium Channel KZM1

PLoS Biology (2010)

Suseno Amien Irina Kliwer Mihaela L. Márton Thomas Debener Dietmar Geiger

Species-preferential osmotic pollen tube burst and sperm discharge in maize involve induced opening of the pollen tube-expressed potassium channel KZM1 by the egg apparatus-derived defensin-like protein ZmES4.

Double fertilization

Egg cell

Gamete

10.1371/journal.pbio.1000388

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Citations (222)

The Pore of Plant K⁺ Channels Is Involved in Voltage and pH Sensing: Domain-Swapping between Different K⁺ Channel α-Subunits

The Plant Cell (2001)

Stefan Hoth Dietmar Geiger Dirk Becker Rainer Hedrich

Plant K(+) uptake channel types differ with respect to their voltage, Ca(2)+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3/(p)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H(+) and Ca(2)+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca(2)+ insensitive, extracellular protons and Ca(2)+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca(2)+ regulation and for the rectification of voltage-dependent K(+) uptake channels are located within the channel pore.

10.1105/tpc.13.4.943

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Citations (44)

The CIPK23 protein kinase represses SLAC1‐type anion channels in Arabidopsis guard cells and stimulates stomatal opening

New Phytologist (2023)

Shouguang Huang Tobias Maierhofer Kenji Hashimoto Xiangyu Xu Sohail Mehmood Karimi

Guard cells control the opening of stomatal pores in the leaf surface, with the use of a network of protein kinases and phosphatases. Loss of function of the CBL-interacting protein kinase 23 (CIPK23) was previously shown to decrease the stomatal conductance, but the molecular mechanisms underlying this response still need to be clarified. CIPK23 was specifically expressed in Arabidopsis guard cells, using an estrogen-inducible system. Stomatal movements were linked to changes in ion channel activity, determined with double-barreled intracellular electrodes in guard cells and with the two-electrode voltage clamp technique in Xenopus oocytes. Expression of the phosphomimetic variant CIPK23T190D enhanced stomatal opening, while the natural CIPK23 and a kinase-inactive CIPK23K60N variant did not affect stomatal movements. Overexpression of CIPK23T190D repressed the activity of S-type anion channels, while their steady-state activity was unchanged by CIPK23 and CIPK23K60N . We suggest that CIPK23 enhances the stomatal conductance at favorable growth conditions, via the regulation of several ion transport proteins in guard cells. The inhibition of SLAC1-type anion channels is an important facet of this response.

10.1111/nph.18708

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Citations (12)

Open stomata 1 (OST1) kinase controls R–type anion channel QUAC1 in Arabidopsis guard cells

The Plant Journal (2013)

Dennis Imes Patrick Mumm Jennifer Böhm Khaled A. S. Al‐Rasheid Irene Marten

Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell S-type anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata' phenotype. Given the fact that guard cells express both SLAC- and R-/QUAC-type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R-/QUAC-type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes. Patch-clamp studies on guard cells show that ABA activates R-/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi1-1 and ost1-2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R-type anion channel. These studies indicate that OST1 is addressing both S-/SLAC- and R-/QUAC-type guard cell anion channels, and explain why the ost1-2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.

Wild type

10.1111/tpj.12133

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Citations (188)

A Single-Pore Residue Renders the Arabidopsis Root Anion Channel SLAH2 Highly Nitrate Selective

The Plant Cell (2014)

Tobias Maierhofer Christof Lind S Hüttl Sönke Scherzer Melanie Papenfuß

In contrast to animal cells, plants use nitrate as a major source of nitrogen. Following the uptake of nitrate, this major macronutrient is fed into the vasculature for long-distance transport. The Arabidopsis thaliana shoot expresses the anion channel SLOW ANION CHANNEL1 (SLAC1) and its homolog SLAC1 HOMOLOGOUS3 (SLAH3), which prefer nitrate as substrate but cannot exclude chloride ions. By contrast, we identified SLAH2 as a nitrate-specific channel that is impermeable for chloride. To understand the molecular basis for nitrate selection in the SLAH2 channel, SLAC1 and SLAH2 were modeled to the structure of HiTehA, a distantly related bacterial member. Structure-guided site-directed mutations converted SLAC1 into a SLAH2-like nitrate-specific anion channel and vice versa. Our findings indicate that two pore-occluding phenylalanines constrict the pore. The selectivity filter of SLAC/SLAH anion channels is determined by the polarity of pore-lining residues located on alpha helix 3. Changing the polar character of a single amino acid side chain (Ser-228) to a nonpolar residue turned the nitrate-selective SLAH2 into a chloride/nitrate-permeable anion channel. Thus, the molecular basis of the anion specificity of SLAC/SLAH anion channels seems to be determined by the presence and constellation of polar side chains that act in concert with the two pore-occluding phenylalanines.

10.1105/tpc.114.125849

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Citations (70)

Site- and kinase-specific phosphorylation-mediated activation of SLAC1, a guard cell anion channel stimulated by abscisic acid

Science Signaling (2014)

Tobias Maierhofer Marion Diekmann Jan Niklas Offenborn Christof Lind Hubert Bauer

Kinases from three different families can activate an anion channel that helps plants tolerate drought stress.

10.1126/scisignal.2005703

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Citations (187)